This invention relates to bag filter apparatus that is adapted to receive gas carrying a quantity of dust or other particulate matter and permit clean gas only to pass therethrough while retaining the particulate matter on the surface of the bag filter apparatus. To remove collected dust from the surface of the filter, a blast of compressed air is then exhausted into the open end of a filter bag to momentarily reverse the flow of gas therethrough and cause a reverse flexing of the bag and removal of the collected dust therefrom. To amplify the action of the blast of compressed air, a venturi is usually spaced above the end of the filter bag and aligned with the blast of cleaning air. Inasmuch as an apertured tube sheet separates the dust laden inlet gas from the clean outlet gas, the venturi is carried by said tube sheet and it opens outward toward the source of compressed cleaning air. To prevent each bag from collapsing when subjected to the flow of dust bearing gas to be cleaned, wire frames or cages are inserted into each bag, thus providing a structural support therefor.